If you've ever boiled eggs, you've probably noticed that sometimes a grey rim appears on the yolk.
Some may think that it is undesirable to eat such a product, but there is no reason to worry, says Yulia Arkhipova, an expert at the online publication BelNovosti.
Why does the yolk change color?
The change in colour of the yellow core of the egg is the result of heat treatment and is not a sign of a spoiled product.
The grey rim appears due to a chemical reaction: during cooking, protein molecules stick together and sulphur is released. The latter turns into hydrogen sulphide, which in turn comes into contact with the iron in the yolk. As a result, iron sulphide is formed – that very grey colour.
To sum it up: if you took boiled eggs out of the saucepan and after removing the shell you found a grey yolk, you can safely eat them.
You cannot eat eggs that have been boiled for more than 20 minutes - prolonged boiling leads to an increase in the release of hydrogen sulfide, as a result of which the yolk acquires a blue-green color.
High levels of the substance can cause poisoning and exacerbation of gastrointestinal diseases.
Expert: Julia Arkhipova
